Description

The burden of proof is always on the person asserting something. Shifting the
burden of proof, a special case of Argumentum ad
Ignorantiam, is the fallacy of putting the burden of proof on the person who
denies or questions the assertion. The source of the fallacy is the assumption
that something is true unless proven otherwise.

Burden of Proof is a fallacy in which the burden of proof is placed on the
wrong side. Another version occurs when a lack of evidence for side A is taken
to be evidence for side B in cases in which the burden of proof actually rests
on side B. A common name for this is an Appeal to Ignorance. This sort of
reasoning typically has the following form:

Claim X is presented by side A and the burden of proof actually rests on
side B.
Side B claims that X is false because there is no proof for X.

In many situations, one side has the burden of proof resting on it. This side
is obligated to provide evidence for its position. The claim of the other side,
the one that does not bear the burden of proof, is assumed to be true unless
proven otherwise. The difficulty in such cases is determining which side, if
any, the burden of proof rests on. In many cases, settling this issue can be a
matter of significant debate. In some cases the burden of proof is set by the
situation. For example, in American law a person is assumed to be innocent until
proven guilty (hence the burden of proof is on the prosecution). As another
example, in debate the burden of proof is placed on the affirmative team. As a
final example, in most cases the burden of proof rests on those who claim
something exists (such as Bigfoot, psychic powers, universals, and sense data).

Arguments of this form assume that since something has
not been proven false, it is therefore true. Conversely, such an argument
may assume that since something has not been proven true, it is therefore
false. (This is a special case of a false dilemma, since it assumes that all
propositions must ether be known to be true or known to be false.) "Lack of proof is not proof."

The fallacy occurs
when it's argued that something must be true, simply because it hasn't been
proved false. Or, equivalently, when it is argued that something must be false
because it hasn't been proved true.

(Note that this isn't the same as assuming something is false until
it has been proved true. In law, for example, you're generally assumed innocent
until proven guilty.)

Examples

Bill: "I think that we should invest more money in expanding the
interstate system." Jill: "I think that would be a bad idea, considering
the state of the treasury." Bill: "How can anyone be against highway
improvements?"

Bill: "I think that some people have psychic powers." Jill: "What is
your proof?" Bill: "No one has been able to prove that people do not have
psychic powers."

"You cannot prove that God does not exist, so He does."

Since you
cannot prove that ghosts do not exist, they must exist.

Since
scientists cannot prove that global warming will occur, it probably
won't.

Fred said that he is smarter than Jill, but he didn't prove
it, so it must be false.

There is no proof that fish feel
pain, therefore they don't

"Of course the Bible is true. Nobody can prove otherwise."

"Of course telepathy and other psychic phenomena do not exist. Nobody has
shown any proof that they are real."

In scientific investigation, if it is known that an event would produce
certain evidence of its having occurred, the absence of such evidence can
validly be used to infer that the event didn't occur. It does not prove it with
certainty, however.

"A flood as described in the Bible would require an enormous volume of
water to be present on the earth. The earth doesn't have a tenth as much
water, even if we count that which is frozen into ice at the poles. Therefore
no such flood occurred."

It is, of course, possible that some unknown process occurred to remove the
water. Good science would then demand a plausible testable theory to explain how
it vanished.

Of course, the history of science is full of logically valid bad predictions.
In 1893, the Royal Academy of Science were convinced by Sir Robert Ball that
communication with the planet Mars was a physical impossibility, because it
would require a flag as large as Ireland, which it would be impossible to wave.
[Fortean Times Number
82.]

"OK, so if you don't think the grey aliens have gained control of the US
government, can you prove it?"

Rebuttal

Identify the proposition in question. Argue
that it may be true even though we don't know whether it is or
isn't.